Acaricides impair prey location in a predatory phytoseiid mite

The use of predatory mites as the sole management tactic in biological control programmes frequently does not fully and reliably prevents damage of phytophagous mites on plants. Therefore, as an alternative, the integration of predatory mites with acaricides can provide more effective control of phytophagous mites than that of the predators only. However, for such integration, acaricides minimal negative impacts on predatory mites are required. In this study, we evaluated the sublethal effects of three acaricides on the foraging behaviour of Neoseiulus baraki (Athias‐Henriot) (Acari: Phytoseiidae) in a coconut production system. The acaricides were assessed for interference with the location of prey habitat using a Y‐tube olfactometer and for interference with the location of the prey colony within the habitat using a video‐tracking system. In addition to the choice of odour source, the time required and the distance walked to make the choice were assessed. The acaricides tested were abamectin, azadirachtin and fenpyroximate. The predatory mite preferred coconuts infested with the coconut mite Aceria guerreronis Keifer (Acari: Eriophyidae) over uninfested coconuts when not exposed to acaricides. However, when exposed to acaricides, the predator did not distinguish between infested and uninfested fruits. When exposed to abamectin, N. baraki spent more time resting and walked greater distances before making the choice of an odour source. Thus, the acaricides impair the ability of the predatory mite N. baraki to locate a prey habitat and to locate a prey within that habitat. The acaricides differentially affected prey foraging by interfering with odour perception.     

A new control strategy for nematodes of sheep using chlamydospores of a fungus,Clonostachys rosea f. rosea,and an ethanolic extract of a plant,Ananas comosus

An experiment was conducted at Ukulinga Research Farm using 24 Merino sheep to test a combination of plant Ananas comosus (Ac) and fungus Clonostachys rosea (Cr) in controlling nematode parasites. Four treatments were assigned: 100 mg kg^?1 body weight (BW) ethanol extract of Ac, 1 g of Cr product kg^?1 BW, the combination of both treatments (AcCr), and a Control. Sheep within a treatment were paired and penned in individual paddocks, and rectal faecal samples were taken for counting of eggs per gram (EPG) of faeces and third-stage (L3) larvae. Grass samples were taken every 21 days for counting of L3 larvae. A. comosus and AcCr reduced (P < 0.001) EPG. A. comosus, C.rosea and AcCr reduced (P < 0.001) L3 counts. The efficacy of treatments increased with time (P < 0.001). C. rosea and AcCr reduced (P < 0.001) L3 on grass. In conclusion, AcCr is better at controlling nematodes than either Ac or Cr individually.     

A simulation model of biological control of social wasps (Vespinae) using mermithid nematodes

Abstract

The nematode (Pheromermis spp.) is a potential biocontrol agent for wasps (Vespula spp.) in countries where invasive populations of wasps cause serious economic, social, and conservation problems. Using a simulation model previously developed for hornets, which belong to a genus with a similar biology to Vespula, we investigated the possibility of using nematodes as a biological control agent. The model wasp colony was exposed to different simulated levels of nematode infection during colony development, and the final number of wasp sexuals produced recorded. The model predicted that early and high levels of wasp infection had the greatest effect on reducing sexual production. However, even colonies with high (80%) levels of infection were still able to produce some sexuals, indicating that wasp colonies are resilient to infections. The model identified several key areas needing further research, including the effects of nematodes on the behaviour and physiology of wasps, of lengthening the infective period, and of increasing infection levels in both the wasps and intermediate transport hosts.     

Biological control of soil-pathogenic nematodes infecting mungbean using Pseudomonas fluorescens

The addition of organic matters to soil has been explored as an alternative means of nematode control under field conditions. Several oil-seed cakes of neem (Azadirachta indica), castor (Ricinus communis), groundnut (Arachis hypogeae), linseed (Linum usitatissimum) and sunflower (Helianthus annuus) were found to be highly effective in reducing the multiplication of soil-pathogenic nematodes Meloidogyne incognita, Rotylenchulus reniformis, Tylenchorhynchus brassicae, etc. The plant growth parameters such as plant weight, per cent pollen fertility, number of pods per plant, root-nodulation and chlorophyll content of mungbean increased significantly. The multiplication rate of nematodes and number of root-galls were less in the presence of Pseudomonas fluorescens as compared to its absence. Damage caused by the nematodes was further reduced when P. fluorescens was added along with the oil-seed cakes. Neem cake was found most effective in combination with P. fluorescens.     

Simple mass‐rearing technique of a predatory mite Gaeolaelaps aculeifer (Canestrini) (Acari: Laelapidae)

We developed a simple mass‐rearing technique for a soil‐dwelling predatory mite Gaeolaelaps aculeifer. The rearing container consists of two (inner and outer) plastic boxes. The inner box contains rice husks, and is placed inside the outer box which contains a small amount of water. This system is useful to keep high humidity within the inner box and to prevent mites escaping from the box. The prey mite Tyrophagus putrescentiae was also reared in a similar way using rice bran and provided to G. aculeifer once a week. Rearing condition within the inner box were maintained at 25 ± 1°C, 95 ± 5% relative humidity. In this double box system, G. aculeifer was rapidly grown and overpopulated within two weeks while another predatory mite Stratiolaelaps scimitus require four weeks rearing period. This technique help farmers improve biological control efficacy of soil pests in greenhouse as well as open field cultivation.     

A method to assess the effects of pesticides on the predatory mite Phytoseiulus persimilis (Acari Phytoseiidae) in the laboratory

Phytoseiulus persimilis Athias-Henriot (Acari Phytoseiidae) is a major predator of Tetranychus urticae (Acari Tetranychidae). The performance of P. persimilis in controlling T. urticae may be altered by pesticides used to manage other pests. Therefore, knowledge of the side-effects of pesticides is essential for IPM. A number of laboratory methods were suggested to evaluate pesticide side-effects on predatory mites. Most methods assess residual effects only, and a number of them are characterised by high predator escape rates from experimental units. A method aimed at evaluating the topical and residual effects of pesticides on P. persimilis is herein described. Mites were treated by microimmersion and then reared in holding cells, on bean leaves previously dipped in a pesticide solution. Three insecticides (pyrethrins, spinosad and thiamethoxam), an insecticide-acaricide (abamectin), and two fungicides (azoxystrobin and tolylfluanide) were evaluated. The strain of P. persimilis used for evaluation was collected from unsprayed vegetable plants. All the pesticides affected the survival and fecundity of P. persimilis. Pesticides did not affect the egg-hatching of P. persimilis females exposed to pesticides. Pyrethrins and abamectin proved to be more toxic than other pesticides, and thiamethoxam was more toxic than spinosad, azoxystrobin and tolylfluanide. The escape rate from experimental units was lower than 5% in all trials. Additional experiments were performed on P. persimilis eggs by dipping leaves with eggs in the pesticide solution. None of the pesticides affected egg survival. Semi-field trials conducted on potted bean plants obtained results similar to those reported in laboratory trials.     

Impact of nC24 agricultural mineral oil deposits on the searching efficiency and predation rate of the predatory mite Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae)

Walking activity, walking straightness, walking speed and searching efficiency of the predatory mite Phytoseiulus persimilis Athias-Henriot were measured on French bean leaf discs that were sprayed with either distilled water, or one of 0.25%, 0.50% and 1.00% w/w aqueous emulsions of an n C24 agricultural mineral oil (AMO). There was no significant difference in percentage of time that mites spent walking in the control (water-sprayed) conditions and in any of the oil treatments. Walking paths were significantly straighter in the oil treatments than in the control, but differences among the oil treatments did not differ significantly. Walking speeds in the oil treatments were significantly slower than in the control and decreased with increasing oil concentration. Deposits of oil at all concentrations significantly suppressed searching efficiency in comparison with control, and searching efficiency in the 1.00% oil treatment was significantly lower than in the 0.25% oil treatment. First predation of P. persimilis on AMO-contaminated eggs of two-spotted mite ( Tetranychus urticae Koch) on unsprayed leaf discs was significantly delayed in all oil treatments in comparison with the control. However there was no significant effect on the overall predation rate. In the tests of P. persimilis predation on AMO-contaminated T. urticae eggs on sprayed leaf discs, the number of first predation occurrences in the first hour was significantly lower in 0.50% and 1.00% oil treatments than in the control. Overall predation rates were significantly reduced by oil but they did not differ significantly among the oil treatments.     

Effect of prey density on behaviour and development of the predatory mosquito,Toxorhynchites towadensis

The effect of prey density on feeding behaviour, killing behaviour, and development of the predatory mosquito,Toxorhynchites towadensis, was investigated in the laboratory. The number of prey consumed per larva increased toward an upper asymptote as prey density increased. Prey consumption curves during fourth instar were concave at low prey densities but convex at high prey densities. This phenomenon was not observed during other instars. Killing without consuming any part of prey occurred at prey densities of 20 per container and over. The number of prey killed but not consumed increased linearly with the number of unconsumed prey in the container. Prey acquisition behaviour was not affected by prey densities during the prepupal period. Developmental time from first instar to adult emergence decreased with increasing prey densities, but remained constant at densities of 10 per container and over. Adult size increased with increasing prey densities but there was no effect at prey densities of 20 and over.     

Hibernation of predatory arthropods in semi-natural habitats

Non-crop habitats provide important resources for natural enemies. Many natural enemies hibernate in non-crop habitats, from which they may colonise arable fields in the spring. Spring colonisation ensures annual repopulation of the crop with natural enemies, allowing them to keep pace with the development of pest populations. The availability of non-crop habitats can, therefore, be crucial to successful conservation biological control. We quantified the density of overwintering natural enemies near organic Brussels sprout crops in five different non-crop habitats (short grassy field margin, herbaceous field margin, herbaceous field margin under a tree line, ditch and forest). Soil and litter samples of non-crop habitats were taken at two sites. One site was located in an open agricultural landscape, the other in a landscape dominated by mixed forest. Insects belonging to Staphylinidae, Araneae, Carabidae, Coccinellidae and Dermaptera were the most abundant. Mean densities of predatory arthropods were higher in the open agricultural landscape (290 predators m⁻²) than in the forested landscape (137 predators m⁻²). Herbaceous habitat types supported the highest densities of overwintering predators (up to 400 predators m⁻²), whereas densities in the forest were lowest (10 predators m⁻²). These results indicate that herbaceous non-crop habitats are important refugia for predators and may play a vital role in conservation biological control. Handling Editor: Arne Janssen.     

New citriculture system suppresses native and augmented entomopathogenic nematodes

Since its first detection in 2005, the bacterial disease huanglongbing (HLB or citrus greening) has emerged as a critical threat to the citrus industry in Florida. An “Advanced Production System” (APS) could mitigate the impact of HLB by bringing citrus trees into production more quickly and economically than conventional citriculture methods. However, unlike conventional practices, APS fertigates plants daily, thereby changing the soil properties in ways that might impact soil biota. We tested the hypothesis that changes to soil properties caused by APS would affect the abundance of native entomopathogenic nematodes (EPNs) and/or the survival of augmented EPNs. The densities of organisms at different trophic levels were measured by real-time qPCR in three experiments conducted in an ongoing field experiment. Target organisms included 6 entompathogenic nematodes, 5 nematophagous fungi (NF) and a phoretic bacterium, Paenibacillus sp. Soil properties, free-living nematodes and citrus fibrous roots were also measured. Compared to soil under conventional citriculture (CC), APS increased soil pH and Mg content, while reducing the electrical conductivity, and content of K, Mn and Fe. The naturally occurring EPN Steinernema diaprepesi was 5 times less abundant in APS plots where these nematodes were more heavily encumbered by the phoretic bacterium Paenibacillus sp., which limits the foraging success of EPNs. In general, when EPNs were augmented in either treatment, fewer Steinernema riobrave than Heterorhabditis indica were recovered and recovery of both species declined rapidly over time. As seen with native S. diaprepesi, fewer augmented S. riobrave were recovered from APS plots in two of the three experiments, whereas the management system did not affect the recovery of H. indica. More of some endoparasitic and trapping NF were recovered from soil augmented with S. riobrave than with H. indica. However, variation in the responses of NF to the management systems suggests that these NF species were not primarily responsible for the steinernematid responses to APS. Although APS has the potential to reduce EPN populations and exacerbate herbivory by subterranean pests such as the root weevil Diaprepes abbreviatus, additional study of the physical causes of this effect may reveal ways to avoid the problem.     

A new method for studying population genetics of cyst nematodes based on Pool‐Seq and genomewide allele frequency analysis

Cyst nematodes are important agricultural pests responsible for billions of dollars of losses each year. Plant resistance is the most effective management tool, but it requires a close monitoring of population genetics. Current technologies for pathotyping and genotyping cyst nematodes are time‐consuming, expensive and imprecise. In this study, we capitalized on the reproduction mode of cyst nematodes to develop a simple population genetic analysis pipeline based on genotyping‐by‐sequencing and Pool‐Seq. This method yielded thousands of SNPs and allowed us to study the relationships between populations of different origins or pathotypes. Validation of the method on well‐characterized populations also demonstrated that it was a powerful and accurate tool for population genetics. The genomewide allele frequencies of 23 populations of golden nematode, from nine countries and representing the five known pathotypes, were compared. A clear separation of the pathotypes and fine genetic relationships between and among global populations were obtained using this method. In addition to being powerful, this tool has proven to be very time‐ and cost‐efficient and could be applied to other cyst nematode species.     

天敌瓢虫种群遗传学及其在生物防治中的应用

天敌瓢虫常在农业生产的生物防治中被广泛引进和使用。这种使用过程往往会导致天敌瓢虫在遗传水平的改变,并最终影响到其生物防治的使用效果和本地生态多样性。对天敌瓢虫种群遗传学的研究,有助于我们认识甚至预测这种遗传改变的规律和生态机制,从而为生物防治计划的优化提供理论基础。本文介绍了种群遗传学的研究方法,分析在生物防治中促进天敌瓢虫遗传改变的因素,以及几种常见的天敌瓢虫种群演变情况,并讨论种群遗传学在天敌瓢虫研究的未来方向。     

A new analytical method of studying post-synaptic currents.

A powerful methodology for analyzing post-synaptic currents recorded from central neurons is presented. An unknown quantity of transmitter molecules released from presynaptic terminals by electrical stimulation of nerve fibers generates a post-synaptic response at the synaptic site. The current induced at the synaptic junction is assumed to rise rapidly and decay slowly with its peak amplitude being proportional to the number of released transmitter molecules. The signal so generated is then distorted by the cable properties of the dendrite, modeled as a time-invariant, linear filter with unknown parameters. The response recorded from the cell body of the neuron following the electrical stimulation is contaminated by zero-mean, white, Gaussian noise. The parameters of the signal are then evaluated from the observation sequence using a quasi-profile likelihood estimation procedure. These parameter values are then employed to deconvolve each measured post-synaptic response to produce an optimal estimate of the transmembrane current flux. From these estimates we derive the amplitude of the synaptic current and the relative amount of transmitter molecules that elicited each response. The underlying amplitude fluctuations in the entire data sequence are investigated using a non-parametric technique based on kernel smoothing procedures. The effectiveness of the new methodology is illustrated in various simulation examples.     

A new integrated method for analyzing heart mechanics using a cell-hemodynamics-autonomic nerve control coupled model of the cardiovascular system

A model of the cardiovascular system coupling cell, hemodynamics, and autonomic nerve control function is proposed for analyzing heart mechanics. We developed a comprehensive cardiovascular model with multi-physics and multi-scale characteristics that simulates the physiological events from membrane excitation of a cardiac cell to contraction of the human heart and systemic blood circulation and ultimately to autonomic nerve control. A lumped parameter model is used to compute the systemic and pulmonary circulations interacting with the cardiac cell mechanism. For autonomic control of the cardiovascular system, we used the approach suggested by Heldt et al. [2002. Computational modeling of cardiovascular response to orthostatic stress. J. Appl. Physiol. 92, 1239–1254] (Heldt model), including baroreflex and cardiopulmonary reflexes. We assumed sympathetic and parasympathetic pathways for the nerve control system. The cardiac muscle response to these reflex control systems was implemented using the activation-level changes in the L-type calcium channel and sarcoplasmic/endoplasmic reticulum calcium ATPase function based on experimental observations. Using this model, we delineated the cellular mechanism of heart contractility mediated by nerve control function. To verify the integrated method, we simulated a 10% hemorrhage, which involves cardiac cell mechanics, circulatory hemodynamics, and nerve control function. The computed and experimental results were compared. Using this methodology, the state of cardiac contractility, influenced by diverse properties such as the afterload and nerve control systems, is easily assessed in an integrated manner.     

A dynamic model for the evolution of sabrecat predatory bite mechanics

The ability of sabretoothed felids to achieve sufficiently high bite forces for predation at extreme gape angles has been the subject of decades of debate. Previous studies have indicated that bite forces in derived sabretoothed felids would have been low, but that they were probably augmented by head depressing muscles. However, bite mechanics is a dynamic process, and mechanical properties change with changes in gape angles. In this study, I present the first comprehensive model of bite mechanics, vector angles, and forces about the temporomandibular joint at gape angles from occlusion to maximal inferred gape in sabretoothed felids. Primitive sabrecats (Machairodus, Paramachairodus) appear broadly comparable to extant large felids (Panthera, Puma), but derived sabrecats in the groups Homotherini (Amphimachairodus, Homotherium, Xenosmilus) and Smilodontini (Megantereon, Smilodon) are often substantially different from either of the former. The ability of the mandibular adductors to generate torque changes with gape angle, indicating that previous models fail to capture potentially important differences in bite function. Inferred muscle sizes and the angles of effective torque from individual adductor fibres in derived sabrecats are different from those of primitive sabrecats and extant large felids, but they had evolved a number of compensatory adaptations for maximizing force output at the canine and carnassial, primarily changes in muscle fibre angles and more compact crania. Inferred outforces at the canines and carnassials were comparable amongst all groups at low gape angles, but at extreme gape angles outforces would have been low, supporting previous hypotheses of head flexor contribution during initial stages of the killing bite in sabrecats. Mandibular adduction in extant carnivores is a complicated pattern of differences in twitch tension and electromyographical activity at different gape angles, and inference of maximal isotonic bite forces from reconstructed mandibular adductor sizes in fossils will give estimates primarily suitable for comparative purposes. Potentially, derived sabrecats could have evolved differences from extant felids in adductor histochemistry or pinnation angle of individual fibres. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 162 , 220–242.     

Effects of entomopathogenic nematodes on the spruce web‐spinning sawfly Cephalcia arvensis panzer and its parasitoids in the field

Field tests were conducted in the Asiago Forest, Venetian Prealps (Italy) to evaluate the efficacy of nematode strains (Heterorhabditis sp. HL 81 Steinernema carpocapsae IS 230 S. feltiae C = bibionis,) IS 389 S. kraussei SK) against the spruce web‐spinning sawfly Cephalcia arvensis. Soil applications of 100 juveniles cm^‐2 of S. feltiae and S. kraussei resulted in 56% and 36.4% reduction of emergences of sawfly, respectively, when performed before the mature larvae drop and enter the soil. The effectiveness of S. feltiae becomes 32.3% if the nematodes are applied when the larvae have already prepared their chambers. S. feltiae parasitized more females and long‐term diapausing individuals than S. kraussei. The two most effective strains (IS 389 and SK) seem to be well adapted to low temperature, which is likely to be the most important limiting factor for nematode activity in the mountain spruce forests. An ichneumonid parasitoid (Xenoschesis fulvipes,) was strongly affected by S. feltiae, resulting in 66.6% reduction of emergences. Another ichneumonid Ctenopelma lucifer, seems to be less affected than X. fulvipes by the nematode application.     

A new method of deploying entomopathogenic fungi to control adult Aedes aegypti mosquitoes

A new system for deployment of fungus‐impregnated black cloths was tested against Aedes aegypti. A “PET trap” was placed in a test chamber to evaluate attractiveness to female A. aegypti with black cloths covered in adhesive film or adhesive film only for 24 and 48 hr. Traps with fungus (Metarhizium anisopliae and Beauveria bassiana)‐impregnated black cloths were tested against female mosquitoes for different time periods (3 h to 48 hr) in the chambers. Traps were then tested under intradomicile conditions against sucrose and blood‐fed insects. Experiments were carried out to ascertain the minimum number of PET traps need to be deployed per test room and to test the effect of different periods of exposure to traps. Exposing the insects for 24 and 48 hr to a PET trap with adhesive film + black cloth resulted in higher rates of trapped mosquitoes (38.6% and 68%, respectively) when compared with adhesive film only (6% and 12.6%, respectively). Both fungal species were effective at reducing survival rates when mosquitoes were exposed to traps for 24 hr or 48 hr. Lower exposure times did not significantly alter survival rates when compared to controls. The results showed that five traps or three traps per room were equally effective in reducing mosquito survival rates when testing both fungal species. The results for sucrose‐fed insects showed significant reductions in survival when exposed to M. ansiopliae or B. bassiana for 24, 48 or 120 hr when compared to control survival, with the lowest survival rates seen following 48‐ or 120‐hr exposures. Survival of blood‐fed mosquitoes exposed to fungus‐impregnated traps for 48 hr was not significantly different to the controls; however, longer exposure times significantly reduced survival rates. PET traps could be an effective system for deploying fungus‐impregnated cloths in residences, facilitating cooperation of volunteers and reducing distribution time.